1. Field of the Invention
This invention relates to a transducer for generating ultrasonic waves to be used in an ultrasonic device, and more particularly to a transducer for generating ultrasonic waves in a liquid medium.
2. Description of the Prior Art
Even if a medium is optically opaque, as long as the medium is acoustically transparent, inspection by acoustic imaging through the medium is possible just like inspection by x-ray. Ultrasonic imaging through optically opaque media is applicable to medical diagnoses, microscopes, non-destructive inspections, inspections of submarine conditions, studies of earthquakes, and the like.
Heretofore, a number of proposals have been made on ultrasonic transducers by using various converting means, such as acoustic phase plates, annular arrays, acoustic lenses, light-sound transducers, and the like. In fact, however, there is still a need for improvement in focusing acoustic waves for the ultrasonic imaging.
To meet such need, the inventor has proposed an apparatus comprising an interdigital electrode means disposed on the surface of a piezoelectric member, so as to radiate ultrasonic beams from the interdigital electrode means by applying an AC voltage to the electrode means while keeping the electrode means in contact with a liquid. In this case, the thickness of the piezoelectric member is sufficient for exciting a surface wave (Rayleigh wave).
The aforesaid technique, however, has a shortcoming in that, due to the fact that the delicate interdigital electrode vibrates while being in contact with the liquid, mechanical and chemical protection has to be provided for the electrode.